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Re: Gap Losses


From: 	Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: 	Wednesday, August 27, 1997 11:11 PM
To: 	tesla-at-pupman-dot-com
Subject: 	Re: Gap Losses

Hi Greg,
 
> From:   Greg Leyh[SMTP:lod-at-pacbell-dot-net]
> Sent:   Wednesday, August 27, 1997 1:19 PM
> To:     Tesla List
> Subject:    Re: Gap Losses
> 
> Malcolm Watts wrote:
> 
> 
> >             Greg asked....
> 
> > > Well, I know that 5.3 ohms is too low for a 4-gap rotary, and I suspect
> > > that 50 ohms is pushing the high side for most gap systems, even the ones
> > > with a zillion static gaps in series.  My rule of thumb at this time is:
> > >
> > > Zchar = 4 ohms X number of series gaps in primary switch.
> > >
> > > I would be interested to know where yours (and others) Zchar values fall,
> > > for your favorite 2-coil systems.
> > > -GL
> > 
> > My mini coils with the first transfer loss reported had Zp on the
> > order of 50 Ohms. I am shooting for 100 Ohms in a new design I have
> > been commissioned to build for display purposes.
> 
> Congrats on the commissioned piece!  Your client should count his lucky stars
> for finding a world-class Tesla coil expert so close to home!

That is a very handsome compliment. Thank you but I must point out 
that coiling at your power levels (or the other big names on the list)
is rather unlikely for me (unless they pay me to do it of course in 
which case I will be glad I've archived yours and their posts). 

> Upon further thought, I realized that my above rule of thumb would only be
> optimal within a fixed range of primary currents, say 2500 to 3000A.  As the
> primary current is reduced, the gap resistance goes up.  This increase in
> resistance at lower operating currents would necessitate an increase in Zp,
> in order to preserve the primary Q.  So 100 ohms might be OK after all.
> What was your reasoning for choosing 100 ohms?

Since I have the opportunity, I decided it would be a good idea to at 
least find out whether there was a significant benefit over 50 Ohms 
at the 200W-odd level. I may be forced to reduce this to use a bigger 
primary cap to get more bang at reduced BPS anyway. I'll post on the 
results as things progress.
    BTW, the same guy is now asking for a second and considerably 
more powerful one. He was initially interested in <= 2 foot 
because of space considerations. Time to roll up the sleeves at last 
:)

Malcolm